A tower crane is a fixed lifting machine made of a vertical mast, a slewing unit and a horizontal or luffing jib. It is the symbol of building sites: from housing to skyscrapers, bridges and power plants, the tower crane lifts steel, concrete, formwork, precast elements and building materials to where they are needed, often for months or years on the same site. Its advantage over mobile cranes is height and reach combined with a small footprint: a tower crane stands on a few square metres of ground and covers a circle up to 80 metres or more in radius.
Brief History of Tower Cranes
Cranes have been used in building since antiquity, from Roman treadwheel cranes to the wooden cranes of medieval cathedral sites. Steel tower cranes appeared in the early 20th century, but they were heavy and slow to erect.
The modern tower crane is closely linked to post-war reconstruction in Europe. In 1949, German master builder Hans Liebherr received the patent for the TK 10, a mobile tower crane that was easy to transport, quick to erect and affordable for builders. It was the foundation of the Liebherr Group and a model for a new generation of cranes. In the same period, French manufacturers, notably Potain, developed the top-slewing tower cranes that became the standard for larger building sites.
From the 1960s onwards, climbing systems allowed cranes to grow with the building, and flat-top designs without a tower head, introduced in the 1980s and 1990s, made it easier to work with several cranes on one site. Today, tower cranes are digitally controlled, connected to fleet management systems and increasingly powered by site grids or batteries.
Parts of a Tower Crane
- Foundation or base: a concrete foundation with anchors, a cross base with ballast, or a rail-travelling undercarriage.
- Mast (tower): lattice sections bolted or pinned together to reach the required height.
- Slewing unit: a slewing ring and motors that rotate the upper part of the crane 360 degrees.
- Operator’s cab: usually at the top of the mast, next to the slewing unit. Many cranes can also be operated by radio remote control.
- Jib (boom): the horizontal or luffing arm that carries the load. On horizontal jibs, a trolley runs along the jib to change the working radius.
- Counter-jib: the rear arm carrying the counterweights and, often, the hoist winch.
- Tower head (A-frame): on hammerhead cranes, the peak above the slewing unit that supports the jib ties.
- Hoist, trolley and slewing mechanisms, controlled by frequency inverters for smooth movements.
- Safety devices: load moment limiter, maximum load limiter, anemometer, working-area limitation and anti-collision systems.
Types of Tower Cranes
Hammerhead (Top-Slewing Saddle-Jib) Cranes
The classic tower crane, with a tower head and tie bars supporting a horizontal jib. A trolley moves the load along the jib. Hammerhead cranes are efficient and offer high capacities at long radii.
Flat-Top (Topless) Cranes
A horizontal jib without a tower head. With no parts above the jib, several cranes can work at different heights with overlapping areas, and the jib is quicker to assemble. Flat-tops are now the most common type on many European sites.
Luffing Jib Cranes
The jib is raised and lowered to change the radius, instead of using a trolley. Because the jib can be raised almost vertically, luffers need very little space to slew. They are the standard crane for dense city centres, high-rise towers and sites where airspace over neighbouring properties is restricted.
Self-Erecting Cranes
Compact cranes that unfold themselves from a transport position, often in less than an hour and without an assist crane. They are used on housing, small commercial buildings and renovation work, and many are towed on their own axles.
Special Cranes
Heavy-duty tower cranes for power plants, bridges and shipyards; rail-travelling cranes; and hydraulic climbing cranes used inside the core of skyscrapers.
Climbing and Tying In
Tower cranes grow with the building in two main ways:
- External climbing: a climbing frame lifts the upper part of the crane so that new mast sections can be inserted. The mast is tied to the building at intervals for stability.
- Internal climbing: the crane stands inside the building core and climbs through the floors as the structure rises, using hydraulic climbing collars. This allows very tall buildings to be served by relatively short masts.
Reading a Load Chart
A tower crane’s capacity is not a single figure. It depends on the radius: the crane can lift its maximum load only close to the mast, and the capacity falls as the load moves toward the jib tip. Manufacturers therefore quote maximum capacity, maximum jib length and tip load (the capacity at the end of the jib), together with the load moment, usually in tonne-metres. When choosing a crane, planners start from the heaviest and furthest lift on the site, typically precast elements or concrete buckets far from the mast.
Size Classes
| Class | Typical maximum capacity | Typical use |
|---|---|---|
| Self-erecting | about 1 to 10 t | Housing, small buildings |
| Small and medium top-slewing | about 4 to 12 t | Residential and commercial buildings |
| Large top-slewing | about 12 to 25 t | High-rise, precast, infrastructure |
| Heavy-duty | 25 t and above, up to several hundred t | Power plants, bridges, heavy industry |
Figures are indicative.
Main Manufacturers
- Liebherr, the largest European manufacturer, from self-erecting to heavy-duty cranes.
- Potain (Manitowoc), a pioneer of top-slewing and self-erecting cranes.
- Terex tower cranes, now part of Raimondi, and Raimondi itself, with its flat-top and luffing ranges.
- Comansa, a specialist in flat-top cranes.
- Wolffkran, known for luffing jib cranes.
- Jaso, Saez, Cattaneo and FM Gru in Southern Europe.
- Zoomlion, XCMG and Yongmao from China.
Main Uses
- Residential, office and commercial buildings.
- High-rise towers and skyscrapers.
- Precast concrete and modular construction.
- Bridges, dams and infrastructure.
- Industrial and energy plants.
- Shipyards and precast factories.
Safety
Tower crane safety depends on correct planning, installation and operation:
- Foundations and erection must follow the manufacturer’s instructions and an engineer’s design, with qualified erection crews.
- Wind: cranes are taken out of service above set wind speeds. When out of service, the jib is released to weathervane freely with the wind.
- Load limiters prevent overloading, and working-area limiters stop the crane entering restricted zones such as schools, roads or rail lines.
- Anti-collision systems are essential when several cranes overlap.
- Inspections are carried out after erection, at regular intervals and after extreme weather.
- Competence: operators, slingers and signallers must be trained and certified according to local regulations.
Trends and Technology
- Electrification and grid power: tower cranes are already electric; the focus is on energy efficiency, recuperation and battery units for sites with weak grid connections.
- Digital fleet management and remote diagnostics.
- Camera systems on the hook to give the operator a view of blind lifts.
- Remote operation from ground-level cabins, being introduced on some sites to improve comfort and safety.
- Automation of repetitive lifts in precast and modular construction.
Key Terms
- Jib: the horizontal arm that carries the load.
- Counter-jib: the arm opposite the jib that carries the counterweight.
- Trolley: the carriage that runs along the jib and moves the load in and out.
- Mast: the vertical tower, built from sections.
- Slewing: rotation of the upper part of the crane.
- Hook height: the maximum height of the hook below the jib.
- Radius: the horizontal distance from the centre of the mast to the hook, on which lifting capacity depends.
Frequently Asked Questions
How does a tower crane grow taller? By inserting new mast sections with a climbing frame (external climbing) or by climbing through the building core (internal climbing).
What happens to a tower crane in strong wind? Operations stop above a set wind speed, and the slewing brake is released so the jib turns freely with the wind, reducing loads on the structure.
Flat-top or luffing jib? Flat-tops are simpler and economical on open sites. Luffers are chosen where space is tight and the jib must not pass over neighbouring properties.
How is a tower crane dismantled? Usually in reverse order to its erection: the mast is lowered section by section if it climbed, then a mobile crane removes the jib, counter-jib and remaining parts.
Why do tower cranes weathervane when not in use? At the end of the shift the slewing brake is released so that the jib can turn freely with the wind. This reduces the load on the structure, which is why an idle tower crane can often be seen slowly turning.
How does the operator reach the cab? On most cranes the operator climbs a ladder inside the mast. Some tall cranes are fitted with a lift to reduce the climb.
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